Process for applying deposits having lubricant properties to workpieces

ABSTRACT

An improved process for applying dry-lubricants to solid surfaces with control over the lubricant thickness. The process depends on an initial electrolytic degreasing step followed by electrodeposition of known molybdenum compounds under definite selected conditions. The compounds are then treated with H2S in an autoclave, at 300 p.s.i. and less than 140* C.

United States Patent [72] Inventors Jean-Leon Spehner;

Roger l-laug; Hans Hoffman, all of c/o Dow Corning Gmbll, Munich, Germany [21] Appl. No. 36,501

[22] Filed May 11, 1970 [45] Patented Dec. 7, 1971 [32] Priority May 12, 1969 [33] Germany [31] P19 24 263.8

[54] PROCESS FOR APPLYING DEPOSITS HAVING LUBRICANT PROPERTIES TO WORKPIECES 5 Claims, No Drawings [52] U.S. Cl. 204/37 R, 204/29, 204/45 R [5 1] Int. Cl. C23b 5/52 [50] Field of Search 204/32 R,

[56] References Cited UNITED STATES PATENTS 2,902,4 l 7 9/1959 Brophy et al. 204/37 R Primary Examiner-John H. Mack Assistant Examiner-W. l. Solomon Attorneys-Robert F. Fleming, Jr., Laurence R. Hobey and Howard W. Hermann PROCESS FOR APPLYING DEPOSITS HAVING LUBRICANT PROPERTIES T WORKPIECES The deposition of dry-lubricants to metal surfaces is a wellknown art covered by many methods. For instance, it is well known that the surfaces of metal workpieces can be drylubricated by tumbling and/or rubbing in molybdenum disulfide powder. It has been determined, however, that the resulting film has a relatively short use life.

In another process, the surfaces of metal articles are coated with bonded coatings containing solid lubricants mixed with binding agents. This process can provide workpieces with layers of lubricant less than p. thick which is highly desirable in the industry. The process, however, is expensive and the lubricant coatings also suffer from a relatively short use life.

US. Pat. No. 2,905,574 has disclosed a process whereby a layer of molybdenum previously deposited on the metal workpiece, is converted into molybdenum disulfide by sulfurization in an alkaline melt. Also molybdenum disulfide can be deposited on workpieces as a result of thermal decomposition of tetrathiomolybdates.

These known processes have several disadvantages, which our disclosure seeks to avoid. For instance, high temperatures required for the sulfurization process changes the workpieces structurally and hence the quality of the end-product may be reduced. The deposits obtained are generally too thick or too thin, so that the dimensions of the coated workpieces vary considerably and modification has to be made. Moreover, the adhesion and subsequent use life of the workpieces prepared by the above procedures, are not satisfactory.

Some of these disadvantages have been overcome by applying thin, firmly adhering layers of chalcogenides of molybdenum and/or tungsten to metal or nonmetal articles by electrodeposition of molybdenum or tungsten oxyhydrates and then subsequently reacting the latter with gaseous or vaporous sulfides selenides, or tellurides for l to 300 hours at 60 to 200 C. and 30 to 600 p.s.i.

Still another process which is said to overcome the above disadvantages is a process whereby workpieces, still moist from the electroplating step, are subjected to, first, warm air and then to an inert cleansing gas used to cleanse the chalcogenizing chamber. The workpieces are then reacted in the chalcogenizing chamber with a mixture of fresh chalcogenizing chamber with a mixture of fresh chalcogenizing gases and unused chalcogenizing gases from previous cycles.

Lastly, an attempt has been made to overcome the above disadvantages by depositing metallic molybdenum or tungsten on the workpieces electrolytically and reacting it with hydrogen sulfide at a pressure of approximately 400 p.s.i. and temperatures of approximately 60 to 125 C. for 30 to 1 hours, according to the deposit thickness desired. The deposition of the pure metals, however, is not reproducible, so that, the desired thickness of the film, which of course, depends on the thickness of the pure metal deposit taking part in the reaction, is also not reproducible. Moreover, this process suffers from blistering and poor adhesion of the deposits.

The desired lubricant film must adhere finnly, be long lasting in service, even when the film is required to be very thin, such as in the structural elements with little bearing clearance and/or narrow tolerances. In service the films should withstand radioactive radiation and, the process for producing the deposits must be suitable for coating large quantities of small workpieces economically.

The object of this invention is to provide workpieces having metal surfaces with dry-lubricating deposits which have low coefiiceients of friction even under extreme stresses, and which can withstand high temperatures and can have a long servie life. It is a primary object to provide a method of producing solid lubricant coatings which are superior to heretofore known coatings of this type.

These objects can be attained in accordance with the present invention by the following procedural steps:

a. The workpieces are electrolytically degreased;

b. deposition of the molybdenum compounds is then carried out for 2 to 10 minutes at a voltage of 3 to 7 volts and a current density of 0.03 to 0.06 amps/in;

c. the workpiece containing the electrodeposited film is then introduced into an autoclave; the existing air is removed from the autoclave and the autoclave is then filled with hydrogen sulfide to a pressure in the range from 142 to 427 p.s.i. at a temperature in the range from to 140 C.

The invention, it can be observed, combines electrolytic degreasing with electrodeposition of the molybdenum compound under definite, selected conditions while the reaction of the electrodeposited layer with hydrogen sulfide is also carried out under definite selected conditions of temperature and pressure.

Features (b) and (c) represent procedures which surprisingly give the desired result. The choice of conditions for electrodeposition and subsequent reaction of the deposited layer gives the desired result only when combined with electroyltic degreasing.

In accordance with the above, the preferred ranges for the reaction are 265 to 325 p.s.i. for pressure, to C. for the temperature and 4 to 10 reaction time. If the temperature exceeds C., the dry-lubricant film detaches itself on cooling. The preferred reaction time is 6 to 8 hours.

In the process, the workpiece forms the cathode and electrodeposition of the molybdenum compound on the work piece produces a layer consisting of oxide-containing molybdenum compounds and not of pure molybdenum. The chemical formula of the oxides has not been precisely determined, because the material is complex. If the electrical current density and voltage remain constant, the quantity of molybdenum compound deposited in unit time decreases. This is believed to be a result of passivation effects which have not been clarified as yet.

In may cases, the molybdenum compounds deposited on metal surface by means of process of the instant invention do not adhere. In that event, two alternatives are proposed:

1. before electrodeposition of the molybdenum compounds, a layer of iron 3 to 5 p. thick should be electrolytically deposited on the workpiece from an iron salt solution at a voltage of 10 to 12 volts and a current density of 0.3 to 0.6 amps/in, or

2. the metal surface of the workpieces should be electrolytically activated in an aqueous bath, using a direct currentof 10 to 12 volts and a current density of 0.6 to 1.2 amps/in.

Steels which cannot be directly coated with a firmly adhesive layer can be provided with very firmly adhesive layers of the molybdenum compound if, in accordance with the instant invention, these layers are electrodeposited from a solution which contains not only a soluble molybdenum compound but also a soluble chromium compound and preferably fluorosilicic acid (H SiF and 11 80 The process according to the invention, which is suitable for producing lubricant layers from sulfur compounds of molybdenum, can also be used for producing lubricant deposits from selenium and/or tellurium compounds of molybdenum. However, these deposits do not have any technological advantages over those obtained from sulfur compounds of molybdenum, However, these deposits do not have any technological advantages over those obtained from sulfur compounds or molybdenum, and they are more costly and, in the case of selenium compounds, highly poisonous.

The invention will be illustrated with reference to the examples.

EXAMPLE 1 Rings and travelers as used for spinning man-made fibers were electrolytically degreased. The degreasing bath was an aqueous solution containing per liter:

*80 g. sodium boroheptonate 60 g. sodium hydroxide 30 g. sodium carbonate 25 g. trisodium phosphate 5 g. sodium pyrophosphate *A sequestering agent for metal ions. A complex sold manmade the trademark of Bowmanol BH in the form of an aqueous solution.

The electrodes were made from sheet iron.

The voltage was 12 volts and the degreasing time 2 hours. Subsequently, at a current intensity of 3.5 amps, a voltage of 6 volts and a current density of 0.27 amps/m an underlayer was obtained by minutes treatment in a bath containing, per liter;

250 g. chromic acid 150 g. sodium molybdate 12 g. sulfuric acid 32 g. fluorosilicic acid and then cleansed.

A 3 y. layer of the molybdenum compound was then applied to this underlayer at a current intensity of 1.5 amps, 7 volts, current density 0.06 amps/sq. in. over a treatment period of 5 minutes, from a solution containing, per liter;

120 g. ammonium formate 30 g. ammonium molybdate 25 cc. concentrated ammonium solution and having a pH of 6.7 to 7.5. The electrodes were made from high-grade steel.

The workpieces coming from the bath were cleansed with distilled water, dried in acetone and then wrapped in aluminum foil. They were then placed in an autoclave which was evacuated by means of a vacuum pump, twice cleansed with hydrogen sulfide and then filled with hydrogen sulfide at a pressure of 285 p.s.i.. The autoclave was then heated to 130 C. and the reaction took place for 8 hours. The workpieces were cooled overnight, and after the excess pressure subsided the autoclave was opened and the workpieces removed.

When these rings and travelers were used to spin man-made fibers, no fouling of the fibers occurred. Whereas spinning rings having deposits obtained by the process heretofore disclosed had only four times the life of untreated spinning rings those having deposits obtained by the process according to the invention had twelve times the life.

EXAMPLE 2 Piston rings tend to jam in the groove and have a tendency to jam the piston. Residues from combustion stick fast to the piston rings. By electrolytically degreasing the piston rings as described in example 1 and by depositing the molybdenum compound (without depositing an underlayer) from the last bath described in example 1, at 5 volts and 1.5 amps for a period of 5 minutes, and then causing a reaction at 140 C. with an initial hydrogen-sulfide pressure of 290 p.s.i. over a period of 6 hours in an autoclave, a solid lubricant layer 1 p. thick was applied. This lubricant layer prevented the piston from jamming and the combustion residues from adhering. Layers applied by the process revealed in the heretofore disclosed prior art were unsuitable because they were not uniformly. thick, and they caused the piston rings to jam in their grooves immediately.

EXAMPLE 3 Screws and nuts made from high-grade steel, for particle accelerators, where extreme cleanness is required, were coated by the process according to the invention. A precise torque had to be obtained in order to preserve the high vacuum in the particle accelerator, and the workpieces had to be resistant to radioactive radiation. Coatings obtained by the process described in U.S. Pat. No. 2,902,417 did not adhere firmly, but flaked off during screwing and jammed.

in accordance with the present invention, degreasing was carried out and an underlayer was applied at 5 volts and a current intensity of 3 amps for a treatment time of 3 minutes from a bath containing per liter;

250 g. ferrous sulfate 40 g. ferrous chloride 20 g. ammonium chloride and then cleansed. The molybdenum compound was then applied in 5 minutes from a bath containing, per liter;

120 g. ammonium formate 30 g. ammonium molybdate 25 cc. ammonia solution at 5 volts and 1.5 amps. The conversion rnto the lubricant deposit then took place in an autoclave as described in example 1. Firmly adhering, resistant coatings were obtained.

Example 4 The application of lubricant layers to threaded spindles by means of bonded coatings did not ensure accurate running, due to the irregular thickness. After electrolytic degreasing, as described in example 3, an underlayer was applied to iron, and the molybdenum compound was deposited onto this underlayer under the same conditions as in example 3, and then reacted with H 8. The threaded spindles ran accurately.

EXAMPLE 5 Traditional lubricants produced undesirable vapors which had very undesirable effects in ball bearings in tunnel kilns, e.g., japanning kilns. Lubricant coatings applied by the process according to the invention did not have this disadvantage, and they gave running times of 4 months without requiring additional lubrication, whereas coatings produced by the process disclosed in U.S. Pat. No. 2,902,417 ceased to be effective after only 1 week. in this case, the treatment according to the invention consisted of electrolytic degreasing as already described, activation of the ball bearings at 10 volts and a current density of 1.2 amps/in. for 1 minute, in a bath containing 20 percent sulfuric acid. The molybdenum compound was then applied during a 10 minute treatment with a current of 5 volts and 1.5 amps in a bath containing per liter;

g. ammonium formate 30 g. ammonium molybdate 25 cc. concentrated ammonia solution. The workpieces were then placed in an autoclave, which was evacuated, filled with hydrogen sulfide up to a pressure of 256 p.s.i. and then heated to 120 C. for 10 hours.

That which is claimed is:

1. 1n the process for applying dry-lubricant deposits to metal surfaces of workpieces, said workpieces having cathode polarity during the process and said workpieces being coated by the electrodeposition of molybdenum compounds and subsequently reacted with hydrogen sulfide at a selected high temperature and pressure, the improvement comprising:

a. the workpieces are electrolytically degreased and after degreasing and before electrodeposition of the molybdenum compound, the metal surfaces are activated in an aqueous sulfuric acid bath using direct current of 10 to 12 volts and a current density of 0.6 to l .2 amps/inf.

b. the deposition of the molybdenum compounds is carried out for 2 to 10 minutes at a voltage of 3 to 7 volts and a current density of 0.03 amps/in. to 0.06 amps/inF, and

c. introducing the electrodeposited workpieces into an autoclave, removing the air by evacuation, and subsequently refilling the autoclave with hydrogen sulfide to a pressure of 142 to 427 p.s.i. and reacting at 100 to 140 C.

2. A process as claimed in claim 1, characterized in that, the autoclave is filled with hydrogen sulfide to a pressure of 265 to 325 p.s.i. and the reaction is then carried out by heating the workpieces to to C.

3. A process as claimed in claim 1, characterized in that, after electrolytic degreasing and before electrodeposition of the molybdenum compound, a layer of iron 3 to 5 s thick is electrodeposited at a voltage of 10 to 12 volts and a current density of 0.3 to 0.6 amps/in.

4. A process as claimed in claim 1, characterized in that, after electrolytic degreasing the molybdenum compound is obtained by electrodeposition from a solution containing a soluble molybdenum compound and a soluble chromium compound.

5. A process as claimed in claim 4, characterized in that, the solution used for electrodepositing the molybdenum compound also contains fluorosilicic acid and sulfuric acid. 

2. A process as claimed in claim 1, characterized in that, the autoclave is filled with hydrogen sulfide to a pressure of 265 to 325 p.s.i. and the reaction is then carried out by heating the workpieces to 125* to 135* C.
 3. A process as claimed in claim 1, characterized in that, after electrolytic degreasing and before electrodeposition of the molybdenum compound, a layer of iron 3 to 5 Mu thick is electrodeposited at a voltage of 10 to 12 volts and a current density of 0.3 to 0.6 amps/in.2
 4. A process as claimed in claim 1, characterized in that, after electrolytic degreasing the molybdenum compound is obtained by electrodeposition from a solution containing a soluble molybdenum compound and a soluble chromium compound.
 5. A process as claimed in claim 4, characterized in that, the solution used for electrodepositing the molybdenum compound also contains fluorosilicic acid and sulfuric acid. 